Have bad credit? A run-in with the law? With more employers running background checks, your mistakes can come back to haunt you.

Your boss won't know if you pay your bills late, drive too fast or recently got into a fight at a bar, so long as you do your job and don't let on that anything is amiss. Right?

Think again.

Employers are running background checks on long-standing employees as well as new ones. The number of checks on all workers has tripled during the past eight years, experts said, mostly because of growing security concerns, the technological ease in obtaining the information and its declining costs.

"Most of our clients who re-check do it on an annual basis," said Jason Morris, president of Cleveland-based Background Information Services Inc., whose company charges an average of $66 for a background check.

Morris said most screeners charge $25 to $200 depending on the worker's level of responsibility and volume of business with an employer.

"Rescreening" is one of many reasons employment background checks -- into credit, criminal, driving, education, employment and other records -- are occurring more often. That is intensifying concerns about fairness to workers who may lose out on a job for a bad mark that's outdated, erroneous or -- in the opinion of some -- irrelevant to the position.

ADP Employer Services in Roseland, N.J., said it conducted 4.4 million background checks last year, up 16 percent from 2003 and a threefold increase from 1997.

A 2004 study by the Society for Human Resource Management in Alexandria, Va., showed that 82 percent of the 270 employers surveyed said they investigated backgrounds of potential employees, compared with 66 percent in 1996.

The group also found that 35 percent of employers check into workers' credit histories, a 16 percent increase since 1996.

Workers have little recourse in stopping such checks because federal law allows bosses to conduct them when hiring, promoting or retaining employees. Workers need to provide permission for the background check just once (a few states require permission each time) and it's usually sought during an interview for the job.

The Fair Credit Reporting Act requires employers to tell applicants when they didn't get a job based on the results of a background check. But managers often just say that someone else was more qualified for the job, said Tena Friery, research director for San Diego-based Privacy Rights Clearinghouse, an information and advocacy group for workers.

Even when an employer is open about failed background checks, and applicants can supply proof that their records are incorrect, they have little recourse for getting a job they were denied.

A strong legal case must be made that the employer or background screening firm acted with negligence or willful conduct, said Joe Harkins, employment attorney with Littler Mendelson in Washington, which mostly defends employers.

Job seekers can better prepare for interviews and spotting errors by ordering their credit report annually and even by screening themselves. Capitalizing on the screening frenzy, Careerbuilder.com recently added a self-screening service for $30 to $50.

Melvyn P. Bennett's records tell the truth. The Baltimore 56-year-old was convicted of a felony 25 years ago, and he knows that will count against him. But he gets frustrated when an employer automatically discounts him for a mistake at age 21, when he's had a clean record since, strong references and job experience including tutoring and mentoring kids and owning a painting business.

Tired of the physical work in painting, Bennett sought a new job. Twice he applied for a license from the Maryland Public Service Commission to drive a limousine and taxi. Twice denied, he appealed the decisions. The second time -- with the help of a lawyer -- he was granted his license in September.

"I was very frustrated with the process," he said. "It was like throwing a blanket over people, not really judging them on an individual basis."

But he wants to encourage others like him not to give up trying.

Commission spokeswoman Christine Nizer said she could not comment on a specific case but acknowledged that some applicants are denied their license based on their criminal records. She added that applicants who appeal their case get a hearing before the commission.

"The individual has the ability to bring in extenuating circumstances, character witnesses, anything they think will be helpful in explaining their character and that they are capable of contributing to society in a positive way," she said.

The number of background checks nationwide has grown, experts suggest, because of heightened concerns since Sept. 11, 2001, about terrorism and violence and lower costs thanks to technology.

Considering that 9 percent of background checks reveal something negative or inconsistent from what the applicant or worker told the employer, according to ADP, some bosses hope background checks can head off negligent-hiring charges.